1. Field of the Invention
This invention relates to a method of manufacturing a tube, and in particular to a method of manufacturing an expandable tube.
2. Description of the Related Art
Within the oil and gas exploration and production industry there have been recent significant developments in relation to the use of slotted expandable tubulars. Such tubulars comprise metal tubing sections in which the tubing wall defines a multiplicity of longitudinal overlapping slots. Once run downhole, the tubing may be expanded to a larger diameter, such expansion being accommodated by deformation of the metal in the tubing wall, and with the slots assuming the form of diamond-shaped apertures. Such slotted tubing has seen application as a support for unconsolidated formations, and as the base pipe for expandable sandscreens.
Currently, slotted tubing is manufactured by cutting slots in extruded tube using CNC abrasive water jetting techniques, or in some cases by the use of laser technology; an example of this is described in PCT/GB98/03478. These manufacturing methods produce a very high quality product, but are time-consuming; a 30-40 foot joint of tubing may take three to four hours to machine.
It is among the objectives of embodiments of the present invention to provide a less time-consuming method of producing slotted tubing.
According to one aspect of the present invention there is provided a method of forming expandable downhole tubing, the method comprising the steps of:
providing a tubing section of a first diameter;
forming apertures in the tubing section; and
reducing the diameter of the apertured tubing section.
The reduced diameter tubing section may be subsequently expanded.
The apertures may axially overlap, but need not do so.
The apertures may be formed by any convenient means, most preferably by punching the apertures in the tubing section, which may be accomplished more easily when the tubing is positioned on a punching mandrel. Of course other aperture forming methods may be utilised, including drilling or other cutting methods.
The reduction in diameter of the apertured tubing may be achieved by any convenient method, most preferably by drawing the tubulars through reducing dies or swages.
The apertures may be of any convenient form, including diamond-shaped, circular, square, rectangular, hexagonal, oval or dog-bone-shaped. Typically, the apertures will be oriented and positioned to create an open lattice structure similar to an expanded or partially expanded conventionally slotted tubing. In the reduced diameter tubing, the apertures will generally tend to assume a more longitudinal slot-like form, and in some instances may partially or completely close.
In most metal tubulars, the diameter reduction step will produce a degree of work-hardening, however in many metals, such as low carbon and alloy steels, the extent of work hardening would not be such to create difficulties in re-expansion. However, the reduced diameter tubing section may be subject to annealing, or some other stress-relieving process, to facilitate subsequent expansion.
If desired, the reduced diameter tubing could be flattened and reeled, for example as described in WO00 26500, for transportation and subsequent unflattening.
In further aspects of the invention, expandable tubing may be produced by:
providing tubing; and
forming apertures in the wall of the tubing by parting the material of the tubing.
The parting may be achieved by shearing or punching, and in one embodiment the tubing wall may be passed between appropriate punching rollers.
As the parting of the material, typically a metal, creates little if any waste or scrap, this method may prove more economic than methods in which apertures are formed by removal of material.
In other aspects of the invention, tubing may be produced by:
forming apertures in a sheet of a first width;
forming the sheet into a tube of a first diameter; and
reducing the diameter of the tube.
Alternatively, the width of the apertured sheet may be reduced prior to forming the sheet into a tube.
In another aspect of the present invention, tubing may be produced by:
forming apertures in a sheet by parting the sheet material; and
forming the apertured sheet into an expandable tube.
This aspect of the invention has the advantage that there is no waste material produced in the creation of the apertures.
Preferably, the apertures are created by shearing or punching, for example by being passed between a pair of punch rollers. This will tend to create an uneven sheet, which may be flattened before being formed into a tube.
In the aspects of the invention utilising sheet, the tube may be formed by any convenient method, and the edges of the sheet may be welded, or joined by other methods, for example by means of mechanical fasteners.
The sheet may initially be formed into a flattened tube and subsequently unflattened.
In certain of the above aspects of the invention the tubing may be dipped or coated in a fluid material which subsequently hardens or solidifies, the material filling the apertures in the tubing wall. On subsequent expansion of the tubing the material may tear or elongate. This aspect of the invention may also be utilised in relation to conventional slotted or apertured tubing.
The material preferably closes the apertures in the tubing wall such that the tubing wall is rendered fluid tight, and may be pressure-tight, at least in one radial direction. In particular, where wedge-shaped apertures are formed in the tubing wall, that is where the diameter, width or length of an aperture is greater towards the outer surface of the wall than towards the inner surface of the wall, the tubing wall may be pressure-tight with respect to external pressure; this aperture configuration will occur as a matter of course where for example, vertical or straight-sided apertures are cut in a sheet which is then formed into a tube having a longitudinal seam. The material filling the apertures, for example zinc from hot dip galvanising or an elastomeric coating from spraying the tube exterior with a curable rubber composition, will form wedge-shaped plugs in the apertures, and even relatively soft or ductile material may withstand external pressure as the wedges of material will tend to be pushed down into the apertures. This may facilitate running the tubing into a bore, as the tubing may then be run safely through a lubricator or packing into a pressurised well.
The references above to apertures are primarily intended to refer to openings in the tubing wall. However, those of skill in the art will realise that many of the effects and benefits of the invention may be achieved by only weakening or thinning the tubing wall material, and not necessarily by forming a through passage or complete parting of the material. For example, it may be sufficient to punch the wall to create a line or area of weakness which will subsequently fail or extend to allow subsequent expansion. Of course this offers the advantage that the tubing is, initially at least, pressure-tight.